The saeculum is the 90-year period between Recurrences. It is not completely clear whether it refers to the gap between the beginning of the previous Recurrence and the beginning of the next one, or the end of the previous Recurrence and the beginning of the next one.

It seems that it refers to the latter, as the 1920s Recurrence ended in 1923, and the 2010s started in 2013. This would mean that the 1920s Recurrence started in 1921, as the 1830s ended in 1831, and would also mean that most of the Modernist gods' incarnation was sometime in 1921, matching with the two-year span that would put an end to their lives in 1923.